1. Field of the Invention
This invention relates to a method and a system for lubrication, suitable for lubrication under the adverse conditions, such for example as in a downhole pump and the like used for pumping geothermal water in geothermal power generation.
2. Description of the Prior Art
In general, for lubricating a mechanical system, there has heretofore been adopted a method of sealing off a lubricant. However, particularly, under the severe conditions such as high temperature and high pressure, deterioration of the lubricant is quickened, the performance of the mechanical system is deteriorated, and further, possibilities of occurrences of troubles and damages are increased, so that the reliability is lowered.
In the geothermal power generation which has been popularized in recent years, downhole pumps are used for pumping of high temperature geothermal water. However, when the geothermal water temperature is 200.degree. C. at 400 m underground for example, the temperature of fill oil in the downhole pump reaches 260.degree.-300.degree. C. due to the heating of a motor or the like, so that the pressure applied to the pump reaches 30-50Kg/cm.sup.2. Under the above-described conditions, there is no lubricating oil or insulating oil, which has a service life more than several thousand hours, and, even jet engine oil, which is optimal as a substitute, has a service life of only scores of hours.
As the countermeasure for avoiding the abovedescribed disadvantages, there has been increased the frequency of stopping the mechanical system in operation to change the lubricant, which is resupplied, thus lowering the operating efficiency.
Now, in order to avoid the lowered performance of the mechanical system, there have been practiced the change of lubricant before the lubricant is deteriorated and reaches its service life and the delayed change of a lubricant having a long service life to decrease the frequency of changes of the lubricants. However, when the lubricant is sealed off, or at a portion beyond approach by an operator, inspection cannot be carried out, and further, it is difficult to previously learn the service life varied depending on the use conditions. As a consequence, the change of the lubricant is made rather earlier than the expected service life to avoid occurrence of an obstruction due to the use of the deteriorated lubricants. In this case, there have been such disadvantages, that a lubricant having a long service life is expensive, an impossibility of using up the service life of the lubricant contributes to an increased expense, thus lowering the economics, and moreover, the frequent changing operations lower the operating efficiency and the maintenance.